Homogeneous Grain Research Articles

Optimization of FSP parameters to fabricate AA7075-based surface composites using Taguchi technique and TOPSIS approach

Aluminum alloy-based surface composites processed by friction stir processing with enhanced hardness and impact energy is potentially suitable for aircraft and automotive applications. This behavior is improved by applying design of experiments (DOEs) in finding the suitable combination of process parameters. The influence of tool rotational speed, transverse speed, tilt angle, plunging depth and number of passes on hardness and impact energy are determined via Taguchi. It is identified that No. of pass plays a major contribution based on ANOVA. Single optimal parameter obtained through TOPSIS is employed to fabricate the composites with different volume ratios of WO3 and SiC particulates. Microstructural characterization of all the defect free surface composites depicts wide and homogenous dispersion of reinforcement particulates. Surface hybrid composite specimen comprising both WO3 and SiC particles significantly raises the microhardness to 214VHN attributed to the homogenous dispersion strengthening and grain boundary pinning mechanism. The specimen tends to show enhanced impact energy (12.3 J) due to extensive load bearing capacity of the reinforcements.

Reznitskyite, CaMg(VO4)F, a new mineral from the Tolbachik volcano, Kamchatka, Russia and the first vanadate with a titanite-type structure

AbstractReznitskyite, ideally CaMg(VO4)F, is a new mineral species of the tilasite group from the Arsenatnaya fumarole, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It occurs as zones (usually up to 0.05 mm thick) in crystals of V- and P-containing tilasite or as homogeneous grains up to 0.1 mm across. It was found in polymineralic sublimate encrustations in association with minerals of the svabite–fluorapatite–pliniusite system and the schäferite–berzeliite, tilasite–isokite, wagnerite–arsenowagnerite and udinaite–arsenudinaite series. The mineral assemblage also includes calciojohillerite, diopside, forsterite, titanite, rhabdoborite-(V), rhabdoborite-(W), rhabdoborite-(Mo), ludwigite, powellite, scheelite, hematite, baryte and magnesioferrite. Reznitskyite is transparent or semi-transparent, colourless, with vitreous lustre. Dcalc. = 3.453 g cm–3. Under the microscope, in reflected light reznitskyite is grey, non-pleochroic, with very weak bireflectance (ΔR589 nm = 0.5%) and distinct anisotropy. Reznitskyite is the first vanadate with a titanite-type structure. It is monoclinic, space group C2/c, a = 6.6912(7), b = 8.9395(7), c = 7.0587(8) Å, β = 113.078(13)°, V = 388.43(8) Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern are [d in Å(I)(hkl)]: 3.082(100)(200), 3.250(66)($\bar{1}$12, 002), 2.631(44)(022), 2.854(34)($\bar{2}$02), 2.683(33)(130), 3.686(26)(021), 2.531(25)(220), 1.749(25)($\bar{3}$32, $\bar{2}$04) and 2.344(24)(131). Electron microprobe analysis gave (wt.%) MgO 20.44, CaO 26.83, P2O5 6.24, V2O5 21.09, As2O5 18.97, SO3 0.47, F 9.42, –O=F –3.97, with a total of 99.49. The empirical formula of reznitskyite, calculated on the basis of O+F = 5 atoms per formula unit, is: Ca0.97Mg1.03(V0.47As0.33P0.18S0.01)Σ0.99O3.99F1.01. Reznitskyite is a vanadate analogue of tilasite CaMg(AsO4)F and isokite CaMg(PO4)F. The mineral is named in honour of the outstanding Russian mineralogist Leonid Zinovievich Reznitsky (born 1938) who has made significant contribution to the mineralogy of vanadium.

Effect of forging temperature on the structure, mechanical and functional properties of superelastic Ti-Zr-Nb bar stock for biomedical applications

Ti-Zr-Nb shape memory alloys exhibit a unique combination of properties that make them suitable for bone implants: low Young’s modulus, superelastic behavior, superior corrosion resistance, and non-toxicity of all the constitutive elements. In this study, superelastic Ti-19Zr-14Nb (at.%) alloy was subjected to a combination of radial shear rolling at 900°C and rotary forging in a temperature range from 500 to 700°C to form long-length bar stocks for bone implants fabrication. Features of the grain structure, phase composition, mechanical and functional properties of the long-length bar stocks were analyzed using light microscopy, X-ray analysis, as well as during mechanical and functional tests. It was shown that after radial shear rolling at 900°C, a heterogeneous grain structure was formed over the cross-section of the bar stock, and this structure was inherited after the subsequent rotary forging at 500°C. With an increase in the forging temperature, the structural heterogeneity is eliminated and the grain size increases, while the hardness and strength characteristics of the material decrease. After rotary forging at 700°C, the alloy manifests the best combination of structural, mechanical, and functional characteristics. In this state, the long-length bar stock demonstrates a homogeneous grain structure with a certain fraction of a dynamically polygonized substructure of β-phase, a satisfactory strength (UTS ≈ 580 MPa), a low Young’s modulus (E ≈ 35 GPa), the high difference between dislocation and phase yield strength (Δσ ≈ 280 MPa), and a relatively large amount of superelastic recovery strain (εrSEmax ≈ 3.1%).

Study of the Effect of Quenching on Microstructural and Magnetic Properties of Cu-Doped Mg-Ferrite

Mg1-xCuxFe2O4 (x = 0.0–0.5) was prepared by the double sintering ceramic method, which sintered at 1100°C and 1200°C for 3 hours and investigated for structural, microstructural, and magnetic properties as a function of the Cu content and cooling process. XRD analysis of 1100°C sintered samples revealed that all the samples were crystallized in a single-phase cubic spinal structure. The microstructural and magnetic properties of slow cooled (furnace-cooled) and fast cooled (quenched) Mg-Cu ferrites have been studied using the scanning electron microscope (SEM), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy after sintering at 1200°C. Homogeneous coaxial grains did not form for any furnace-cooled samples, while for the quenched sample, homogeneous grains were clearly visible even without doping with Cu. Substantial grain growth was witnessed by the samples with higher copper content for both cooling conditions, whereas quenched samples possessed a smaller grain size compared to furnace-cooled samples. The saturation magnetization experienced a higher value for quenched samples compared to furnace-cooled samples with increasing Cu content except for x = 0.4. The sextet pattern of Mössbauer spectroscopy confirmed all the samples were ferromagnetic in nature. Chemical shift, quadrupole shift, hyperfine field, and site occupancy of Fe3+ were also obtained using Mössbauer spectroscopy.

Bi-Sn-In phase change material with low melting point and high cyclic stability for thermal energy storage and management

Rapid thermal energy storage and management is of great significance in the fields of energy utilization and sustainable thermal control. In present article, Bi-Sn-In phase change material with low melting point and high cyclic stability for rapid thermal energy storage and management was designed and prepared by static melting method, and thermal properties and thermal management performance of this alloy were further reported. According to microstructure evolution of the alloy from SEM and XRD analyses, thermal cycling promoted a homogeneous microstructure and grain refinement, and the alloy finally transformed to stable phase with BiIn2 and InSn4, so it exhibited excellent chemical stability after thermal cycles. After 200 thermal cycles, the volumetric latent heat and melting point were respectively 233.4 MJm−3 and 58.3 °C, and they were slightly reduced within 2.4%. Thermal conductivity of the alloy gradually increased with thermal cycles, and it was 23.58 W/(m·oC) after 200 thermal cycles. The thermal management performance of the alloy and associated organic materials was measured by thermal infrared images, and the transient temperature response of the alloy can be improved with the increasing of thermal cycles, showing good thermal stability. Compared with organic materials, Bi-Sn-In alloy had close volumetric latent heat and melting point, and it had higher thermal conductivity and thermal stability, therefore it provided better transient temperature response during heating and cooling process.

Homogeneous Grain Boundary Passivation in Wide‐Bandgap Perovskite Films Enables Fabrication of Monolithic Perovskite/Organic Tandem Solar Cells with over 21% Efficiency

AbstractMonolithic perovskite/organic tandem solar cells have attracted increasing attention due to their potential of being highly efficient while compatible to facile solution fabrication processes. One of the limiting factors for improving the performance of perovskite/organic tandem cells is the lack of wide‐bandgap perovskites with suitable bandgap, film quality, and optoelectronic properties for front cells. In addition, the development of low‐bandgap organic bulk‐heterojunction (BHJ) rare cells with extended absorption in the infrared range is also critical for improving tandem cells. This work has carefully optimized mixed halide wide‐bandgap perovskite (MWP) films by introducing a small amount of formamidinium (FA+) cations into the basic composition of MA1.06PbI2Br(SCN)0.12, which provides an effective means to modulate the crystallization properties and phase stability of the films. At optimized conditions, the MA0.96FA0.1PbI2Br(SCN)0.12 forms high‐quality films with grain boundaries homogeneously passivated by PbI2, leading to a reduction in defect states and an enhancement in phase stability, enabling the fabrication of perovskite solar cells with a power conversion efficiency(PCE) of 17.4%. By further integrating the MWP front cell with an organic BHJ (PM6:CH1007) rare cell composed of a nonfullerene acceptor with absorption extended to 950 nm, a tandem cell with PCE over 21% is achieved.

Petrogenesis of post-orogenic Pan-African rare-element granitic pegmatites in the western Arabian-Nubian Shield, Aswan area, southern Egypt

• Aswan pegmatites evolved via fractional crystallization of the parental granitic magma . • The rare-element pegmatites were formed in a post-orogenic setting. • Post-magmatic hydrothermal fluids play an important role in their formation. Pegmatites with rare-element mineralization from the Aswan area in southern Egypt intruded the post-orogenic Pan-African granitic rocks and the associated gneisses. The granitic pegmatites show a regular pattern of concentric zoning and display a weak affinity to the Nb-Y-F (NYF) pegmatite family. These pegmatites consist mainly of K-feldspar, albite, quartz, and subordinate muscovite, accessory minerals include Nb-Ta oxide minerals, monazite-(Ce), xenotime-(Y), zircon, rutile, and magnetite. Field observations combined with the petrography, mineralogy and geochemistry of pegmatites and associated rocks in the Aswan area indicate that the pegmatites evolved via fractional crystallization of the parental granitic magma with an effective role for the post-magmatic alterations. The wide compositional variations of Nb-Ta minerals in term of their major and trace elements reflect the pegmatite formation stages. Primary magmatic generation of columbite-(Fe) occurs as homogeneous grains or showing oscillatory zoning with high Nb/Ta and Fe/Mn ratios. Late ixiolite shows patchy and irregular zoning with high Sc and W replacing the earlier regular texture, indicating metasomatic replacement. Electron microprobe U–Th–Pb dating of monazite from the studied pegmatites yielded post-orogenic Pan-African age of 578 ± 5 Ma, comparable with age of the fine-grained granite in this area, but it is younger than the previously estimated U–Pb zircon age of surrounding the Monumental granites and gneisses (∼600 to 620 Ma). The similarity in age and geochemical characteristics of the pegmatites and the fine-grained granite proved their genetic relationship.

Effect of Sr2+ substitution on the Raman spectrum, phase composition and microwave dielectric properties of CaMg1−Sr Si2O6 ceramics

The Sr-substituted CaMgSi2O6 ceramics (CaMg1−xSrxSi2O6, x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5) were synthesised via solid-state reaction method. The CaMg0.9Sr0.1Si2O6 sample was dense at 1250 °C, and outstanding performance was achieved: εr = 7.85, Q×f = 77,916 GHz (13.65 GHz), and τf = −42.89 ppm/°C. The effects of Mg2+ substituted by Sr2+ on the phase composition, microstructure, lattice vibration and microwave dielectric properties of CaMgSi2O6 ceramics were investigated. The doped Sr2+ with solubility between 0.05 and 0.1 mol promoted the densification and grain growth of ceramics and led to the formation of second phase and red shift of X-ray diffraction peaks and Raman active modes. Density and porosity played an important role in εr. The Q×f value was optimised with homogeneous grain size distribution, high relative density and low full width at half maximum. The τf value was closely related to the second phase and changed nonlinearly with the x value.

Influence of high energy ball milling on structural, microstructural and optical properties of TiO2 nanoparticles

The influence of high-energy ball milling on structural, microstructural, and optical properties of TiO 2 by modifying the nanoparticle size was studied. Five samples were extracted at different milling times (0, 2, 4, 8, and 13 h). The average particle sizes estimated by dynamic light scattering (DLS) were 205, 155.8, 116.8, 82.9, and 82.7 nm at 0, 2, 4, 8, and 13 h, respectively. X-ray diffraction analysis confirmed progressive broadening of the peaks as the milling time elapsed. Besides, a correlation was found between d spacing and the average crystal size. The UV–Vis diffuse reflectance spectra of TiO 2 revealed a decrease in reflectance due to particle size reduction. Similarly, an alteration of the bandgap transition energy was presented, whose values gradually decreased from 2.966 eV to 2.861 eV for the sample without and with the maximum duration milling performed (13 h), respectively. Likewise, the SEM analysis showed a distribution in nanoparticle size that became more homogeneous and smaller average grain size as the milling duration was longer.

Effects of Zn Addition on the Microstructure and Mechanical Properties of As-Extruded Mg-2Al-0.5Ca Alloy

The effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-2Al-0.5Ca-xZn (x = 0, 0.3, 0.6, 0.9 wt.%) alloys were investigated in this work. The results showed that the extruded sheets exhibited a completely dynamically recrystallized microstructure, the grain size was refined, and texture weakening was achieved with Zn addition because of the segregation of Zn atoms on grain boundaries, which suppresses the growth of dynamic recrystallized grains. The addition of 0.6 wt.% Zn improved both the tensile strength and ductility of the as-extruded Mg-2Al-0.5Ca alloy. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed a 0.2% proof stress of 145 MPa, an ultimate tensile strength of 317 MPa, and an elongation of 30.0% along the extruded direction. The simultaneous improvement of strength and ductility was mainly due to the fine and homogeneous grain microstructure and the weakened extrude direction (ED)-tilted texture. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed little in-plane anisotropic tensile properties, with a 0.2% proof stress, ultimate tensile strength, and elongation in the 45° direction of 148 MPa, 299 MPa, and 25.0%, and those in the transverse direction of 148 MPa, 269 MPa, and 16.8%, respectively.

Effect of loading path on grain misorientation and geometrically necessary dislocation density in polycrystalline aluminum under reciprocating shear

Solid phase processing (SPP) is a promising alloy fabrication technique to produce fine and homogeneous grain structures for high-performance alloys. However, there is very limited modeling capability to understand and predict the grain refinement during SPP. In this work, the crystal plasticity theory was used to study elastic–plastic deformation in polycrystalline aluminums under large shear deformation. Two approaches, kernel averaged misorientation (KAM) and grain reference orientation deviation (GROD), were used to assess the grain misorientations. The geometrically necessary dislocation (GND) density was computed with the plastic strain rate. The deformation simulations were carried out under two loading conditions to investigate the effect of loading paths on the evolutions of grain misorientation and GND density. The results show that the regions with high misorientation and GND density first appear near grain boundaries. These regions then extend toward interior grains. The loading path affects plastic deformation accumulation and recovery, hence dislocation evolution and misorientation. Both two- and three-dimensional simulations showed that the spatial and temporal evolutions of GROD, KAM, and GND density are closely correlated, which indicates they all can be used as criteria of grain refinement or recrystallization, the essential information for grain refinement simulations.

Cr-spinel tracks genesis of Co-Fe ores by serpentinite replacement at Bou Azzer, Morocco

Co-Fe arsenide ores are associated to serpentinite with alteration haloes of carbonation and talcification in the Bou Azzer inlier (Central Anti Atlas, Morocco). These Co-Fe rich ores consist mainly of skutterudite and members of the löllingite-safflorite series, associated to accessory Cr-spinel grains. Cr-spinel grains exhibit modal abundance and texture-typology inversely correlated with the proportion of Co-Fe arsenide in both Co-Fe arsenide ores and their hosting alteration haloes in serpentinite. So, Cr-spinel grains exhibit distinct textures depending on their relation with the Fe-Co ore: (1) Type 1A zoned grains, consist of homogenous cores of Cr- and Fe2+-rich Cr-spinel surrounded by ferrian chromite rims, which are usually found in carbonatized and talc-rich serpentinite, and in disseminated Co-Fe arsenide ores. (2) Type 1B zoned grains, consist of porous cores of Cr-Fe hydroxides rimmed by ferrian chromite with rare irregular bands of Cr- and Fe2+-rich spinel. They are exclusively hosted by disseminated arsenide ores from F55 and F7/5 orebody. (3) Type 2 grains, consist of homogenous ferrian chromite hosted in löllingite and, at a lesser extent in calcite, in serpentinite hosted massive and disseminated arsenide ores. (4) Type 3 grains, correspond to partly dissolved ferrian chromite, and Cr-Fe hydroxide, associated to chlorite from disseminated Co-Fe arsenide ores.Type 1A zoned Cr-spinel was produced by an event of ocean-floor serpentinization that affected these mantle rocks during Neoproterozoic times. In contrast, the others three types of Cr-spinel crystals (Type 1B, Type 2 and Type 3) associated to Co-Fe arsenide ores from F/5 and F55 orebody, were produced during the Co-Fe arsenide ore-forming event(s). So, the infiltration of low temperature, highly oxidizing CaCl2-rich hydrothermal fluids through fractures dissolved partially pre-existing serpentinite, while precipitating Co-Fe arsenides ± calcite assemblage. The first sign of mineralizing fluid infiltration is recorded in the zoned Cr-spinel grains by the replacement of homogenous cores (in Type 1A) by Cr-Fe hydroxide, giving rise to zoned Cr-spinel with porous core (i.e., Type 1B). The increase of Co-Fe arsenides precipitation further promoted dissolution of ferrian chromite and Cr-Fe hydroxide (i.e., Type 3) erasing relicts of former grains, nevertheless some homogenous Cr-spinel grains (i.e., Type 2) persist included in calcite and löllingite in disseminated and massive arsenide ores hosted in serpentinite.

Electrochemical synthesis and characterization of self-doped aniline 2-sulfonic acid-modified flexible electrode with high areal capacitance and rate capability for supercapacitors

Polypyrrole and aniline 2- sulfonic acid (CFt/PPy/ASA(0.03) composite was synthesized on carbon felt (CFt) under acid conditions. Here, we report investigated in concentration of ASA on the electropolymerization of the PPy, to improve performance of supercapacitor by a facile and effective one-step electropolymerization method. To form a 3D carbon felt, homogeneous and large grains are grown on the surface with the addition of ASA, which provides high active mass and potential redox materials of pseudocapacitive supercapacitor. The flexible electrode shows a high specific areal capacitance 4000 mF.cm−2 at the scan rate of 10 mV.s−1 and excellent rate capability. A symmetric supercapacitor was also assembled with 1 M H2SO4 electrolyte which delivers a maximum energy density of 18.8 Wh.kg−1 at a power density of 312.5 kW.kg−1, and a maximum power density of 1875 kWh.kg−1 can be reached up while delivering a energy density 2.2 Wh.kg−1. The device displays retention of capacitance performance 82.7% even after 2500 cycles in aqueous electrolyte on the PPy-based materials. Therefore, (CFt/PPy/ASA(0.03) electrode has an important role in practical applications of flexible, wearable and portable electronics.

Texture development and tensile properties of Mg–Yb binary alloys during hot extrusion and subsequent annealing

Ytterbium (Yb) containing magnesium alloys have aroused extensive interest due to their excellent mechanical properties after thermomechanical processing and heat treatment. Unfortunately, the sole effect of Yb addition on the microstructure and mechanical properties of pure Mg matrix remains uncertain to date. In this work, the effects of Yb concentration on the texture development and tensile properties of pure Mg matrix during hot extrusion and the subsequent annealing were systematically investigated. The results revealed that the constitutional supercooling induced by Yb addition refined the as-cast microstructure but exerted a negligible effect on the original columnar grain morphology. When extruded at 300 °C, the dynamic recrystallization (DRX) process was considerably retarded. The in-grain misorientation axes (IGMA) analysis combined with TEM observation indicated that non-basal slips operated with increasing Yb concentration. Specifically, the prismatic <a> slip should be robustly activated in Mg–1.0 Yb extrudate, promoting the formation of the texture with {10–10} plane normal to the extrusion direction (ED), while for the Mg–2.0 Yb counterpart, the increased activity of pyramidal < c + a > slip and the relaxation of basal/< c + a > dislocations generated an ED-tilted texture component. The preferential grain growth dominated the subsequent annealing texture development at 400 °C when a comparable grain size was achieved. An obvious ED-tilted texture intensity with the peak around <–12–13> was observed in Mg–2.0 Yb alloy, which was primarily caused by grains with the basal orientation vanished and with the non-basal orientations intensified due to a higher concentration of Yb solute. Favored by the grain refinement, the Mg–2.0 Yb extrudate exhibited a high tensile yield strength of 304 ± 3.5 MPa, while the subsequently annealed counterpart presented a favorable elongation to failure of 14.8 ± 1.2%, which mainly due to the homogeneous grain structure, weak ED-tilted texture, and dissolution of coarse phases after high-temperature annealing.

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural, and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics.

Undoped Ba(Zr0.9Ti0.1)O3 and rare-earth-doped (Ba1−xRE2x/3)(Zr0.9Ti0.1)O3 (RE3+ = La3+, Sm3+) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr0.9Ti0.1)O3 and formation of perovskite structure with the Pm3̄m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Effect of carrier gas species on the microstructure and compressive deformation behaviors of ultra-strong pure copper manufactured by cold spray additive manufacturing

Cold spray (CS) which has recently become a promising additive manufacturing (AM) technology, was used to fabricate ultra-strong pure copper. In addition, the effects of carrier gas species on the microstructural characteristics, mechanical properties and deformation mechanisms were systemically explored. The CSAM copper manufactured with N2 carrier gas reveals a heterogeneous bimodal microstructure consisting of ultra-fine grains at the particle interface and relatively coarse grains in inner particles. With He carrier gas, a homogeneous grain structure consisting of ultra-fine grains in most areas was obtained. Compressive tests showed that N2 and He carrier gasses enabled ultra-high yield strengths of 340 and 415 MPa, respectively. These values are comparable to severely plastic deformed copper, which has extremely low ductility and shape fidelity. On the other hand, both samples showed a strain-softening phenomenon that does not commonly occur at room temperature. The deformation microstructures revealed that dynamic recovery (DRV) and dynamic recrystallization (DRX) phenomena were generated despite being deformed at room temperature. Based on the above findings, the overall deformation mechanisms according to the carrier gas species in the CSAM copper manufacturing process were discussed. Furthermore, the work hardening and softening behaviors of CSAM Cu are predicted by using a constitutive equation .

Ultra-low dielectric loss lithium-based, temperature stable microwave dielectric ceramics

The low loss and small density of lithium-based microwave dielectric ceramics (MWDCs) make them promising for communication devices such as dielectric filters, antennas, and substrates. In this study, (1- x )[Li 2 Ti 0.98 Mg 0.02 O 2.96 F 0.04 −1 wt%Nb 2 O 5 ]- x Li 3 Mg 2 NbO 6 (LTMN 0.02 -LMN, 0 ≤ x ≤ 0.1) MWDCs fabricated via solid solution reaction were successfully synthesized to obtain a near-zero temperature coefficient of the resonant frequency (τ f ). The X-ray diffraction pattern and Rietveld refinement results showed that a good solid solution was formed and that the phase composition of the LTMN 0.02 system gradually changed from monoclinic to cubic. Scanning electron microscopy images revealed that the microstructure of LTMN 0.02 improved as the LMN content increased. Ultimately, desirable dielectric properties were obtained by sintering at 1220 °C with x = 0.08: ε r ∼18.1, Q × f ∼105,661 GHz, and τ f ∼ + 1.3 ppm/°C. Furthermore, the highest Q × f value (∼131,157 GHz) was achieved in the x = 0.04 composition with relatively homogeneous grains. The high-performance LTMN 0.02 -LMN ceramics developed in this study provide a new alternative material for the dielectric components of communication systems.

Microstructural origin and control mechanism of the mixed grain structure in Ni-based superalloys

Mixed grain structure, as an incomplete recrystallization, should be homogenized and refined by subsequent processing to improve the mechanical properties of the aeroengine components. The microstructural origin and control mechanism is quite necessary for the microstructure homogenizing and grain refining through thermo-mechanical processing. In present research, microstructural origin and control mechanism of the mixed grain structure have been conducted deeply. With the consideration of temperature drop in practical industrial forging, the optimum processing parameters can be determined as 1110–1140 °C/1.0 s−1 to obtain homogeneous equiaxed grains. The microstructure evolution corresponding to the identified optimal parameters, viz., deformation temperature and strain rate, were systematically investigated. Higher dynamic recrystallization (DRX) fraction and coarser DRX grains can be observed at super-solvus temperature deformation (1140 °C). In addition, sub-solvus deformation (1110 °C) shows random orientated distribution while near< 001 > compression texture can be detected in super-solvus deformation. Particular attention was paid to the DRX mechanisms during hot deformation. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occur simultaneously, and the synergistic effect of them contributes to microstructure control. Moreover, DDRX characterized by grain boundary bulging dominants the microstructure control. Progressive subgrain rotation labeled as CDRX can be regarded as an important assistant mechanism. The findings would provide theoretical support for microstructure control of Ni-based superalloys with mixed grain structure, which is of vital importance for components to obtain excellent performance.

Enhanced tensile properties by heterogeneous grain structures and coherent precipitates in a CoCrNi-based medium entropy alloy

A dual heterogeneous structure with both heterogeneous grain structure and coherent L12 nanoprecipitates was obtained in a CoCrNi-based medium entropy alloy (MEA) with chemical composition of Co34.5Cr32Ni27.5Al3Ti3 (in at%). The volume fraction of L12 phase is observed to become higher and the corresponding interspacing becomes smaller after aging, resulting in a more severe heterogeneity. The unaged samples are found to have better tensile properties as compared to those for the CoCrNi MEA with homogeneous and heterogeneous grain structures. The aged samples display an even better synergy of strength and ductility than the corresponding unaged samples. The hetero-deformation-induced hardening plays a more important role in the aged samples than in the unaged samples, especially at the elasto-plastic transition stage, producing higher density of geometrically necessary dislocations for better tensile properties. Multiple deformation twins, stacking faults and Lomer-Cottrell locks are the dominant deformation mechanisms for the unaged samples, while interactions between these defects and L12 nanoprecipitates play important roles in the aged sample, the shearing hardening mechanism is observed for L12 nano-particles.

Purification of aluminium-silicon alloy by electromagnetic directional solidification: Degassing and grain refinement

• An electromagnetic directional solidification process was proposed to purify Al alloy. • Grain refinement and degassing were realized simultaneously. • Effects of the induction current, moving rate, and remelting were investigated. • Both tensile strength and elongation were improved by remelting process. • The mechanism of bubble transfer process was explained by simulation. The grain size and porosity are two significant parameters to evaluate the properties of the Al alloy. In this work, an electromagnetic-field-enhanced directional solidification process hybridized with the remelting treatment was proposed to refine the grain size of Al alloys and at the same time to remove the residual gas in molten alloys. Furthermore, the effects of several factors on the grain refinement and degassing were investigated. The high induction current is effective for the obtainment of the small homogeneous grain size because of the stirring effect. With the increase of the moving rate, the grain size increased and then decreased due to the nucleation effect. The remelting process enables both the grain refinement and H 2 degassing to obtain regular grain orientations. The simulated pressure field, velocity field and H 2 gas volume fraction show the mechanism of the bubble transfer in the liquid Aluminum alloy. The pressure field depicts a sharp pressure gradient on the upper side of the bubble. The velocity field indicates an increase in the velocity maximum in the bubble. The shape evolution process of the H 2 bubble shows the effect of the interface tension.